In recent years, various techniques for efficiently using a limited frequency band have been implemented in a radio communication system. As an example of the techniques, a multiple-input multiple-output (MIMO) technique has been known. With this technique, multiple signal sequences using the same frequency band are simultaneously transmitted via multiple transmission antennas, and the multiple signal sequences are received via multiple reception antennas and then separated from one another.
In a radio communication system using the MIMO technique, the reception side receives the multiple signal sequences in an interference state, and thereafter separates the signal sequences from one another on the basis of differences among propagation channel characteristics of the signal sequences. Specifically, the reception side separates the signal sequences from one another by use of channel estimation values acquired by a channel estimation technique for estimating propagation channel characteristics.
With this MIMO technique, the propagation channel characteristics of the signal sequences can be surely made different from one another by increasing an interval between the installation positions of the antennas, so that the separation performance for the signal sequences (hereinafter, referred to as “signal separation performance”) can be improved. For this reason, a cooperative MIMO technique for simultaneously transmitting multiple signal sequences using the same frequency band to a single radio terminal via multiple antennas of multiple radio base stations (radio communication devices) has been proposed (refer to Patent Document 1).